Brake disc for a vehicle and method for the production thereof

ABSTRACT

The invention relates to a brake disc (BS) for a vehicle, comprising a main body (G) that is made of a metal material, particularly gray cast iron, which has friction surfaces (R) having a coating (B) made of a hard material. 
     According to the invention, the coating (B) is formed from carbides, ceramics, cermet or metals.

The invention relates to a brake disc for a vehicle according to thecharacteristics of the preamble of claim 1. The invention furtherrelates to a method for the production of a brake disc according to thecharacteristics of the preamble of claim 14.

From the state of the art is known, as described in DE 10 2004 016 098A1, a brake disc for a vehicle and a method for producing a brake disc.The brake disc has at least one main body, which carries awear-resistant layer at least partially in the region of its outersurfaces, which layer serves as a friction layer, wherein at least oneintermediate layer is applied as an adhesion-conveying layer and/or as acorrosion protection layer between the main body and at least one outerwear-resistant layer and this at least one intermediate layer is appliedin a galvanic manner.

In DE 10 2005 008 569 A1 is described a friction element and a methodfor its production. In this method, a friction element main body isprovided and a coating is applied. The coating has a melting alloy andis melted on.

From DE 102 03 507 A 1 is known a brake disc for a vehicle and a methodfor its production. The brake disc comprises a main body of a metalmaterial, particularly gray cast iron, which has at least one frictionsurface with a coating of a hard material with a high frictioncoefficient. The main body is turned around the layer thickness in thedirection that is axis-parallel to the axis of the brake disc. Thecoating consists for example of aluminum oxide, diamond or a ceramicmaterial.

In DE 103 42 743 A1 is described a brake disc for a vehicle and a methodfor its production. The brake disc comprises a main body, which carriesa wear-resistant layer at least in the region of the outer surface,which serves as a friction layer and a region of a material for theadhesion-conveyance between the main body and the at least onewear-resistant outer layer, wherein the region of the material for theadhesion-conveyance and the wear-resistant outer layer is formed as atleast one gradient layer, whose composition changes in the layerthickness direction.

From DE 103 45 000 B3 is known a device and a method for producing brakeparts. With the method for producing brake parts, a wear protectionlayer is provided for its annular brake surface, which wear protectionlayer is formed by the surface-side melting on of the carrier materialand mixing of coating material with the melt and is introduced into thecarrier material, wherein the energy entry for the surface-side meltingon of the carrier material takes place by light waves, arcs, plasmaand/or electron beam, and particularly preferred by a laser, effects thesurface to be melted on as radiation energy.

The invention is based on the object to provide an improved method forproducing a brake disc for a vehicle.

The object is solved according to the invention by a method forproducing a brake disc for a vehicle with the characteristics of claim1. Regarding the method, the object is solved by the characteristicsgiven in claim 14.

Preferred arrangements and further developments of the invention aregiven in the dependent claims.

The brake disc for a vehicle according to the invention comprises a mainbody of a metal material, particularly gray cast iron, steel or aluminumalloy, which has friction surfaces with a coating of a hard,wear-resistant material. The coating has hard materials in the form ofcarbides, or oxide ceramics.

The hard materials of carbides or oxide ceramics considerably contributeto an improved wear-resistance and good and constant frictioncoefficients. The carbides or the oxide ceramics are thereby present asbound by a binder phase or a matrix, which are particularly formed byalloys on the basis of Cr, Ni and/or Fe. Particularly Cr and/or Cr/Nisteels are among these.

By means of the solution according to the invention, a cost-efficientbrake disc can be produced, as a large part of the brake disc consistsof cost-efficient gray cast iron. By means of the coating, the brakedisc has however a largely lower wear that a brake disc where thefriction surfaces are also formed of gray cast iron. Furthermore, aweight reduction and a corrosion reduction can be achieved by means ofthis coating.

The solution according to the invention enables an even frictioncoefficient of the brake disc and a reduction of temperatures occurringduring braking, whereby a so-called brake fading, that is, a failure ofthe brake due to overheating can be avoided. By means of a reduction ofvibrations and noises during braking, a comfort increase canadditionally be achieved. By means of the solution according to theinvention, elaborate reworkings for a surface hardening are omittedduring a manufacture.

Embodiments of the invention are explained in more detail by means of adrawing.

It shows thereby:

FIG. 1 a longitudinal section through a brake disc according to theinvention.

FIG. 1 shows a longitudinal section through a first embodiment of abrake disc BS according to the invention. The brake disc BS is formed ofa main body G of a metal material, for example of gray cast iron. Steelor a light metal alloy as for example aluminum can also be used asfurther materials. The friction surfaces R of the brake disc BS have acoating B of a hard material, which acts as a wear protection material.This coating B comprises carbides and/or oxide ceramics as hardmaterials. These coatings can also belong to the material classes ofcermets or metal alloys.

In a first arrangement of the coating, carbides of tungsten and/or ofchromium are incorporated in a metallic matrix of nickel, cobalt and/orchromium.

The part of WC is hereby preferably in the region of 60-85%. (Weightpercent are always meant to be understood with the statement %, unlessstated otherwise.)

The metallic matrix essentially has the object of the binding of theenclosed carbides. The part of the metallic matrix is preferably in therange of 10 to 50%, particularly preferred in the range of 15 to 25%.

Thereby, alloy compositions with a high Co content are of particularimportance for the metallic matrix, so that particularly parts of 8-15%Co, 2 to 6% Cr and 0.001 to 3% Ni and possibly traces of further metalsresult for the coating.

Typical preferred coating compositions are:

-   70-85% WC,-   7-12% Co 10,-   3-5% Cr,-   0.5-2% Ni, and contaminants    or-   75-85% WC,-   7-12% Co 10,-   3-5% Cr,-   0.001 to 1 Ni, and contaminants.

A further embodiment of the coating B of carbides is WCCoCrNi, formedwith a part of about 80 weight percent, cobalt, preferably with a partof about 10 weight percent, chromium, preferably with a part of about 1weight percent.

The Cr can also be present in these coating compositions as partiallyalso bound as carbide.

A further well-suited metallic matrix is coined by a high Ni content. WCand Cr₃C₂ occur as hard materials as essential components of thesecomponents, which together result as a part of 70 to 95% of the coating.

Typical preferred coating compositions are:

-   65-85% WC-   15-30% Cr₃C₂-   5-12% Ni, and contaminants,    or-   70-75% WC,-   18-22% Cr₃C₂,-   5-8% Ni, and contaminants.

A coating B of carbides is for example WCCr₃C₂Ni, preferably formed witha part of about 73 weight percent, chromium carbide, preferably with apart of about 20 weight percent and nickel, preferably with a part ofabout 7 weight percent

A further coating with carbides is formed of a chromium steel. Here, Crcarbides essentially occur as hard materials. The preferred steels havea chromium part of 12 to 22 weight percent. 15-20% Cr are preferred.

A further coating B is formed of oxide ceramics, for example of titaniumoxide (TiO₂) and aluminum oxide (Al₂O₃). The aluminum oxide part ispreferably between 60 weight percent and 97 weight percent and titaniumoxide (TiO₂), preferably with a part between 3 weight percent and 40weight percent. Compositions with 50-60% of Al₂O₃ and 40-50% of TiO₂ areparticularly preferred.

A further coating is a compound material of oxide ceramics in a metalmatrix, often also called cermet. Stainless steel is particularlysuitable as metallic matrix. Particularly suitable stainless steels areCr/Ni steels, particularly 316L or 1.4404. The ceramics is preferablycontained with a part of 50-80, preferably 65 to 75 weight percent, andthe intermetallic matrix preferably with a part of 20-50%, preferably25-35 weight percent. The ceramics preferably consists of aluminum oxide(Al₂O₃) with titanium oxide (TiO₂). The aluminum oxide part in theceramics is preferably between 60 weight percent and 97 weight percentand titanium oxide (TiO₂) preferably with a part between 3 weightpercent and 40 weight percent. Compositions with 50-60% Al₂O₃ and 40-50%TiO₂ are particularly preferred.

By means of a pre-treatment of the main body G of the brake disc BSprior to applying the coating B, for example by grinding the frictionsurfaces R, an optimum coating B and an optimum hold of the coating Bcan be achieved on the main body G.

High speed flame spraying, plasma spraying, cold gas spraying or arcwire spraying can preferably be used as coating methods. The high speedflame spraying is particularly suitable for generating the coating B ofcarbides. The plasma spraying is suitable for generating the coating Bof ceramics, cermet or metal. The cold gas spraying and the arc wirespraying are also suitable for generating the coating B of metal.

With the plasma spraying, a plasma is generated by an arc and a plasmagas flowing through this arc. In a plasma gas flow forming thereby, thecoating material is introduced in powder form, which is melted on by theplasma and is sprayed onto the friction surfaces R to be coated by meansof the plasma gas flow.

With the cold gas spraying, the coating material is sprayed on in powderform onto the friction surfaces R with a very high speed. A relativelylow heated process gas is accelerated to supersonic speed for this byexpansion in a laval nozzle, whereby a gas beam forms. The coatingmaterial is injected into this gas beam. The powdery coating material isthereby accelerated to a speed which is so high that it forms a tightand a rigidly adhering layer when impinging the friction surfaces R tobe coated, also without a melting on beforehand, in contrast to otherthermal spray methods.

With the arc spraying, the coating material is melted on in the shape ofa wire by means of an arc. Spray particles forming thereby are sprayedonto the friction surfaces R to be coated by means of an atomizer gas.

The coating B can further for example also be applied by means of alaser beam, electron beam or induction, wherein the coating material isapplied to the friction surface to be coated for example in powder formand is melted on by means of a laser beam, electron beam or induction.

By means of a variation of method parameters of the mentioned coatingmethods, the coating B can be optimized, so that a coating B adheringoptimally on the main body G with optimum properties can be achieved,that is, a wear- and corrosion-resistant coating B with an optimumnoise, vibration and temperature behavior.

List of Reference Numerals

-   BS Brake disc-   B Coating-   G Main body-   R Friction surface

The invention claimed is:
 1. A brake disc (BS) for a vehicle, comprisinga main body (G) of a metal material, which has friction surfaces (R)with a coating (B) of a hard material, which comprises oxide ceramics,wherein the coating is a compound material of oxide ceramics and metalmatrix with a ratio of 50-80% to 20-50%, and wherein the ceramics isAl₂O₃ and TiO₂, with a ratio of 60-97% to 3-40%, and the metal matrix isCr/Ni steel.
 2. The brake disc (BS) according to claim 1, wherein thecoating (B) is applied to friction surfaces (R) of a main body (G) of ametal material by means of high speed flame spraying, plasma spraying,cold gas spraying or arc wire spraying.
 3. The brake disc (BS) accordingto claim 1, wherein the metal material is gray cast iron.